Insulating exposed floor of addition

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Old 02-02-15, 12:53 PM
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Insulating exposed floor of addition

Hi all, my first post here on the forums. I am looking to insulate the floor of an addition off the back of my (it's really my landlord/boss's house, but he gives me discounts for work I do) house. It is only about 13 ft x 7 ft in size and holds the washer and dryer along with a small bathroom. This is important, because there is currently a cutout for the dryer vent in the floor which is poorly sealed. There are also some pipes and tubes for the hvac systems that sit BELOW the joices. All 3 sides are open, but have lattice wrapping the space. The space below is also about 3 feet in height.

There is currently nothing insulating the floor, and the room is always cold (I really don't know how the pipes don't freeze in that room all the time). The only requirement is that the entire space cannot be walled off completely, as my two basement kitchen windows look out under the addition. I have removed the possibility of treating it like an indoor crawlspace because of this.

So now with that out of the way, my plan is: foaming the dryer vent cutout. inserting fiberglass batts inbetween the joices leaving a few inces from the floor to create an air space. I read a lot about the science of convection, conduction, and radiance, so this sounds like the best route to go if I properly air seal everything, in which I plan on doing. My next step is to enclose the insulation and joices with rigid insulation (not sure if foil faced would be better or not), and then using either plywood or OSB to finish it off. I will put foil tape on the joints of the rigid layer, and also foam the perimeter before the last layer, and then foam again. Any red flags there, please let me know!

My main problem is dealing with the pipes. I want to consider just building out an extra 6 inches below them, and sealing off there. I would just add another layer of fiberglass batts around them. This might not be much work either, as the 1 of the 2 supports runs in a way (perpendicular) as a cut off from that end of the addition, so I need to stop the rigid foam on the other side if it anyway. If anyone has solved a problem like this I would appreciate your feedback. I can provide pictures at a later time if requested. Thanks!!

Nick
 
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Old 02-02-15, 03:08 PM
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Welcome to the forums! Insulating the joist cavities with Roxul Safe 'n Sound will provide more insulative value than the same thickness in fiberglas. I would install the insulation, skip the foam and install plywood under it all. Now, you mention pipes below. That is another can of worms in which pictures would be very beneficial. http://www.doityourself.com/forum/el...your-post.html
 
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Old 02-02-15, 03:50 PM
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Some one really cheaped up on this one, no way in you area should this have been an open foundation!!!
No matter what you do this is always going to be a issue until that area is enclosed.
 
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Old 02-02-15, 04:58 PM
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I'd probably suggest you put rigid foam on the rim joists (all outer perimeters) before doing anything else. Then add Roxul. And then sheath it. If you have additional pipes (pics would help) framing in a chase around them would be pretty easy. The edges of any sheathing you add to the bottom will have to be flashed behind the siding, or they will catch water.

Keep in mind that adding insulation alone isn't going to make it much warmer if there isn't a heat source.
 
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Old 02-02-15, 06:27 PM
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I'm a little further north than any of you and I have had to deal with this same condition several times in my career. Here is what I have done and has worked about as well as can be expected in an open floor situation.

As XSleeper stated, foam sheathing cut to fit and foamed in place at the rim. I use 2" R-max or equal. I then cut 1" R-max to fit between joists and space it below the subfloor by 1"-2" using some wood or foam blocks or strips tacked in place. I then foam seal the edges of that. Then install the fiberglass or rock wool to fill the space. Install 1" or 1-1/2" R-max sealed in a high quality elastomeric sealant at the perimeter. Nail or screw in place with cap nails or screws with fender washers. Apply foam sealant to edge of sheets when making joints and push them tight. Finally, apply plywood or osb screwed into place.

The foam below the floor helps to control conductance through the floor joists and even though DC winters aren't as bad as mine, it definitely helps.

You may have to be a little creative around the perimeter depending on how the siding and sheathing were installed. You want to flash the edges of the foam and osb with some type of aluminum or bendable vinyl trim to protect from water and whatever else.

Your added issue of the pipes has to be looked at carefully as you don't want to prevent heat from migrating to them from above. Think about how you can still do the best job in the floor and not allow any weak point where air can infiltrate the assembly and negate your efforts. You may want to add pipe insulation to help prevent drafts from hitting them in the event you can't come up with an otherwise tight assembly in that area.
 
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Old 02-02-15, 07:11 PM
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Thanks everyone for your inputs. Everything mentioned are things I have put some thought into so that makes me feel better. The addition definitely wasn't a great job... it's an older row home in DC, and I'm assuming the previous owner had it done on top of what was already in place (a deck/porch), however there are concrete steps leading up to the door so that makes me wonder. I will be sure to include pictures, because I would like some more confidence in tackling this job around the pipes and even around the perimeter. I think these little things will make the biggest difference aside from just stuffing some barriers under there. The room is heated (at least I see a vent) but I don't believe the walls are insulated that great. I plan on doing this in conjunction with draft proofing the door so in combination, I am confident there will be a noticeable difference. If I can't get home in the evenings before it's dark, I'll have to wait until Saturday morning to post the pictures.

calvert -- I am originally from PA as well, so I am already noticing a large difference in just a few hours away, added to being in the city. Most notably the last few weeks only getting flurries compared to the inches of snow!

Thanks again everyone. I am looking forward to adding to my DIY list.

Nick
 
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Old 02-09-15, 02:31 PM
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Pics

Hey all, I am back with some pictures from the weekend.
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I didn't quite feel like crawling all the way under, but I figured these would suffice for now. Took some measurements too, 12 ft. x 6 ft., ~3 ft. from the ground. 4 joice gaps of 15 inches each. One smaller gap of about 2 inches on the side away from the house.
 
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Old 02-11-15, 06:38 PM
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With all that mechanical spaghetti fastened to the floor framing it may just be best to have someone spray closed cell foam a few inches thick directly to the underside of the floor. You could also bring it down the joists but I would stop short of totally encasing them. The foam will give you the best air barrier and insulation in view of the complexities of working around everything.

Adding some skirting at the perimeter would at least keep the "polar vortex" from whipping around under there. If you could enclose the piping with some light framework and sheathing and then spray that as well it would help control conductance through that area also.
 
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Old 02-12-15, 11:54 AM
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Thanks for the feedback. Foam definitely seems easy. I would still prefer to box off the piping. Would you recommend foaming the floor, and then also the outside of the encasing of the pipes? Or just one or the other?

My only reservation about doing the whole thing with foam was that I really don't like the way it looks (very minor, I know) so I may prefer to lay some board under there to enclose it. Will there be any consequences to this with the layer of foam between the joices?
 
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Old 02-12-15, 01:12 PM
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If you foam the rim joist perimeter like we talked about before, and then maybe foam between the joists (shove tight to subfloor, then fill the rest with fiberglass or better yet, Roxul,) I'd sheath the bottom with plywood... go right over the top of/around the pipes, and cut a nice hole for the dryer so that it goes straight down through the plywood before turning 90. (use solid duct, not flex.) Then you could always come back and box the pipes in later... the plywood surface will give you something nice and flat to build off of if you wanted to enclose them in a chase. Personally I don't see what the point of that would be. Can't believe those drain pipes don't freeze. Building an insulated chase around them isn't going to help much when they are so far away from the heat source.
 
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